O2 sensor

Thank you for your response.
I don't have catalytic converter and also don't have any codes storied in ECU.
I have checked fuel pressure before change o2 sensors and it was fine.
Last thing is timing. I think if it was timing it could be permanent not temporary problem because I can acceleration good but a minute later it goes bad again and it repeats.

It was about 50 psi.
I'm using o2 sensor spacer for downstream and there is no problem with that and no check engine light or pending code.
I'm troubling with sluggish acceleration now and its intermittent for example when stop at lights then try to accelerate its good but a while after it goes sluggish like its regain its power and lose it.
I have checked everything but find nothing also replace MAF sensor with new OEM one.
Update:
Today I test it first it goes to close loop very soon I mean when coolant temperature was about 40 degrees.
Second I have unplugged both upstream sensors and car accelerate so much better, but I can't believe if my new o2 sensors is defective as well as my previous o2 sensors.
I should mention one more time that there is no check engine light or even pending code in my ECU.

Thank you.
You said 3 things include fuel pressure, catalytic converter and timing.
About fuel pressure as I said it was about 50 psi. For catalytic converter I don't have catalytic converter on my car because I removed it. I did timing about 30k kilometers ago and didn't have any problem since.

As I mentioned, today I unplugged my both upstream o2 and see lots of difference in acceleration, but I don't know what's wrong because they are new and also OEM.

I have torque app on my phone and except crankshaft and camshaft sensor I have checked almost all sensors in my car and they are all in good shape I think, but I can record a video from my sensors data if you want.

I have reset my ECU yesterday but before that it was at 0.
Sometime I see that it goes to -0.8 and -1.6 (i mean 0.8% rich and 1.6% rich) but never stuck for long time on each one and fluctuates between this 3 percentages.

I think if it timing problem it would be permanent problem, but I haven't any noise or idle problem and still I think unplug o2 sensor can't affect timing problem.
What else could be the problem?

Then you think it is timing problem?
I have a p0335 code once that occur with a hiccup but after that it never shows again. I have checked crankshaft position sensor after that but it didn't seems bad at all.
This problem makes me crazy for longer than one year.

It doesn't seem fried or damaged or anything else and its fault code didn't show up again.
I have checked everything I can find in the engine including:
TPS
MAF
Intake air temperature sensor
Coolant temperature sensor
Injectors
Ignition coils
Spark plugs and wires
Fuel pump and filters
But nothing. I mean there was no codes. Checked their resistance with dvm or their values and live dates on torque app.
The only thing that didn't work normally was o2 sensors that I changed them.
But one strange thing is my long fuel trim is the same as before o2 sensors change for both banks even after o2 sensors changed and reset ECU.
Just one thing changed in car behave
with my previous o2 sensors when I started engine from cold start sluggish acceleration was permanent unless I restart engine after restart engine, that sluggish acceleration was gone completely.
But now it's comes and goes even after restarting engine.

So the timing checked everything was aligned and right. Now what do you think?

No the mechanic, checked the belt and tell me nothing is wrong about timing or belt.